The Amazing Cold Frame

If I could only pick one season extending structure for a
home vegetable garden, it would be a cold frame. Incredibly versatile, a simple
cold frame is the key to taking your garden from a two or three-season plot and
turning it into a year round vegetable factory. They are easy and inexpensive
to build and can be constructed from simple, often recycled materials like
scrap wood, straw bales, bricks and old windows.

At its most basic, a cold frame is simply a box with a clear
or translucent top. Its purpose is to trap solar energy from the sun and
provide protection from the outside elements – cold temperatures, rain, wind
and snow. The back of the box is typically taller than the front, which lets
the top of the cold frame sit at an angle. This slope allows maximum sunlight
to enter the structure and will help it shed excess rain and snow.

In our frames, the first seeding of the year begins in mid
to late February when the harshest part of winter has passed and the amount of
daylight is steadily increasing. At this time, I seed any empty areas of the
frames with hardy crops like green onions, carrots, beets, spinach, arugula,
tatsoi, endive and mache. I like to give the soil a boost before sowing, but in
mid-winter, the compost pile is frozen solid. Therefore, I rely on
vermicompost, which I buy in small bags from a local worm farmer and keep
indoors where it won’t freeze.

As the weeks progress into March and spring beckons, more
cold and cool tolerant veggies are seeded into the shelter of the frames –
hardy lettuces, pak choi and mizuna for example. All of these plantings will
provide gourmet salads just in time for Easter!

We continue to harvest through April and May and once the
early spring veggies are done, the cold frames are taken out of production for
two months. June and July are allocated for soil building, where we incorporate
generous amounts of chopped leaves and compost into the earth – I like to add 3
to 4 inches of our homemade compost. It’s also rich in worms, which happily
break down the shredded leaves. If the soil pH has dropped, I add powdered
lime. If you don’t have compost, sow a cover crop in your cold frames, digging
it under a few weeks before you intend to plant.

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By late July and early August, it’s time to start thinking
about fall and winter crops and I begin the process by transplanting
pencil-thick leek seedlings at the back of one of the frames. The winter
carrots are also seeded in late July. They’re a true cold season treat and as
the temperatures drop in late autumn, the long roots get sweeter and sweeter.
In early December, I’ll add a 6-inch layer of straw or shredded leaves to the
carrot frames to further insulate the crop.

As August marches on, I make sure that I have enough seed
for all the hardy salad crops that we like to grow. If not, a last-minute order
goes out to our favorite seed companies. Late August and early September is
seeding season for winter lettuces, mache, claytonia, endive, tatsoi, pak choi,
spinach, Swiss chard, green onions and more. Even herbs like thyme and parsley
do extremely well in a winter cold frame and I move a few plants into the
corners of the structures in early September. To get around the hot
temperatures of August and September that can inhibit germination, I will start
many of my salad crops indoors under my grow lights, moving them into the
garden once they’re a few inches tall.

At the end of September, all the crops for fall and winter
have been seeded or transplanted into our cold frames and from December until
the following May, they’ll provide us with the sights, scents and flavors of
spring each time we lift the covers to harvest.

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